In current Next Generation Networks (NGN) or Internet Protocol (IP) networks, fax can be transmitted in different formats, for example, using T.38 mechanism or simply over voice codecs, such as, G.711. However, the sender side fax device, the receiving side fax device, the sending network, and the receiving network have to agree beforehand on the fax mode that would be used for fax transmission. Only after the mode for fax transmission has been agreed upon, the fax is transmitted from the sender side fax device to the receiver side fax device.
As only that fax mode, which is supported by both the sender side fax device and the receiver side fax device, can be used for the fax transmission, if one of the fax devices only supports fax mode of a lower quality, the fax will be transmitted using lower quality mode only. This lower quality may be further degraded in case of lossy links or networks, or under adverse network conditions. As a consequence, the quality of fax received by the receiver side fax device is much worse than what was originally transmitted from the sender side fax device.